Pre-Test De Guzman, Aaron Choco S. BSME-3C Answer the following questions below. • • • • • What is the difference between direct (DC) current and alternating (AC) current? How are they produced? What is a reversible energy-conversion process? Name a device that have this kind of property. Name the different types of electrical machines. Give description of each type. Name at least five common household appliances or devices that uses electric motor to operate. Describe the purpose of the motor on each particular device. What was Michael Faraday’s basic discovery? What do you think is its significance on motor operation? 1. What is the difference between direct (DC) current and alternating (AC) current? How are they produced? Alternating current (AC) and direct current (DC) are notable for inspiring the name of an iconic metal band, but they also happen to sit right at the center of the modern world as we know it. One of the major differences between the alternating and direct current is that in alternating current the polarity and the magnitude of the current changes at the regular interval of time whereas in direct current it remains constants. A sinusoidal AC can be produced in a generator. The generator has to be driven by a prime mover. It could be anything like a turbine, diesel engine, etc. Other forms of waves can be produced in a wave generator device usually found in labs. DC can be produced by providing a rectifier unit with AC. It also can be produced from batteries or solar cells. 2. What is a reversible energy-conversion process? Name a device that have this kind of property. When we say reversible energy-conversion it is a process where any given electrical machine can convert power in either direction, any machine can be used as either a generator or a motor. One example of it is the Dynamo since it converts electrical energy into mechanical to start a car. And during driving it converts mechanical energy into electrical energy. 3. Name the different types of electrical machines. Give description of each type. A device capable of inter-conversion between electrical energy and mechanical energy is called Electrical Machine. Electrical machines are classified into two main types: 1. Stationary Electrical Machines 2. Dynamic Electrical Machines Stationary Electrical Machines is such kind of machine which does not have any moving parts & they remain stationary throughout its operation. A transformer is a stationary electrical machine, which does not have any moving parts. It is a machine because there is a conversion between electrical & magnetic energy between the windings of the transformer. Dynamic Electrical Machines is type of machines consists of moving parts as well as stationary parts. There are two types of Dynamic electrical machines the electrical motor and electrical generator. Electrical Motor is a type of dynamic machine which converts electrical energy into mechanical energy. Electrical motors generate a mechanical force due to the interaction between the magnetic field and current in a conductor. There are two main types of Electrical motors: DC motor & AC motors. DC Motors: Wherever a current-carrying conductor is placed inside a magnetic field, it experiences a mechanical force. The DC motor operates on this principle. AC Motors: the stator is made up of winding which is connected to the AC voltage supply. It creates a rotating magnetic field. While the Electrical Generators is exactly opposite to the operation of electrical motor. According to faraday’s law, a conductor placed inside a varying magnetic field will experience an induced emf. In other words, moving a conductor in a static magnetic field will induce emf in the conductor. 4. Name at least five common household appliances or devices that uses electric motor to operate. Describe the purpose of the motor on each particular device. The invention of motors is a world-changing event that greatly and irrevocably affected the way we live our lives. Motors have also influenced how we live at home, especially when it comes to doing house chores. Here are five common examples of household appliances and devices that use electric motor technology to operate: 1.Refrigerator- is common household appliance; it needs small motors to operate its compressor. This compresses the refrigerant chemical into a liquid to create the cold temperature that helps preserve fresh goods. 2.Electric toothbrush- This automated wonder that lets us clean our teeth quickly and thoroughly also has a micro motor in it. This makes the bristle head vibrate and spin at the touch of a button. 3.Computer – it is do in fact sport motors, even if at first glance it doesn’t seem to have any moving parts. The motors have to do with its hard disk drives. It ‘spins’ the platters in a drive and read the data stored on them. The cooling fans that wick hot air away from the inside of the unit also requires motors to spin. 4.Microwave oven- There’s also a motor in the microwave oven, a kitchen appliance used to heat leftovers and thaw out frozen goods. It’s mainly in the turntable mechanism that slowly rotates your food as the microwave itself starts the heating process. 5.Washing machine- it needs a heavy-duty motor to be able to do its job. For twin-tub machines that have a washing tub and a spin dryer tub, two motors are needed. The front-loading machines on the other hand generally just make do with one. 5. What was Michael Faraday’s basic discovery? What do you think is its significance on motor operation? The Discovery of Electromagnetic Induction was an enormously important discovery for the future of both science and technology. Faraday discovered that a varying magnetic field causes electricity to flow in an electric circuit. Previously, people had only been able to produce an electric current with a battery. Now Faraday had shown that movement could be turned into electricity – or in more scientific language, kinetic energy could be converted to electrical energy. The Discovery of Electromagnetic Induction has a huge significance on motor operation especially most of the power in our homes today is produced using this principle. Rotation (kinetic energy) is converted into electricity using electromagnetic induction. The rotation can be produced by high-pressure steam from coal, gas, or nuclear energy turning turbines; or by hydroelectric plants; or by wind-turbines, for example. References: i. ii. iii. N. N. Bhargava & D. C. Kulshreshtha (1983). Basic Electronics & Linear Circuits. Tata McGraw-Hill Education Roger S. Amos, Geoffrey William Arnold Dummer (1999). Newnes Dictionary of Electronic (4th ed.). Newnes. p. 83. ISBN 0-7506-4331-5. Chisholm, Hugh, ed. (1911). "Faraday, Michael" . Encyclopædia Britannica. 10 (11th ed.). Cambridge University Press.